Highly probably DNA  selectively adsorbs on cathodic sites of your substrate leading to decrease in cathodic peak

Dear Professor Mustafa Urgen,

Thanks for your response.  i want  to give more clarification in my doubt so that you can give your answer in correct way. In the CV, first i have taken the CV spectra for metal complex in solution  and i added the DNA to the solution then i take the reading. Based on the shift and current intensity we can say the mode of interaction between DNA and complexes.

In the present case the current intensity decreased along with positive shif. It indicate the mode of interaction between DNA and complex is intercalation. (there are many reference reports available for this concept). But here the question is why the current intensity decreases in the cathodic peak, but not in the anodic one.

Is DNA  interaction facilitate the cathodic current (reduction of Cu(II) to Cu(I)) and restrict the anodic current (oxidation of Cu(I) to Cu(II)) ?

If your DNA is anionic and can bind with your metal complex, it is likely that the DNA binds with the Cu(II) complex stronger than the Cu(I) complex, and hence sterically blocks charge transfer to the Cu(II) centre.

Dear Prof. George Zheng chen,

Thanks for your response. Nice and interesting answer. Could you provide any  article related to your answer. It is not necessary that your given article deals with CV studies of  DNA binding . if the article related to your view/ concept that  is fine.

Dear Dr. Kumar:

Well, some situations can exhibit such Picture, but the participation of pH in the “Question” would be major.

Seems that the question stemming of the idea where nucleic acids, which have total negative charge due phosphate group, should migrate to anode (positive pole). In this sense, any DNA accumulations at cathode (negative pole) surface sound estrange. Here, is necessary verify if poles were not noted in inverse way involuntary.

However, in a broad sense, proteic particle being amphoteric compounds can  exhibits positive or negative charge as function of medium pH that lead to possibility of migrates at cathode or anode. At this point emerge some relevance of control of a pH during analysis, via a proper buffered solution. Then, an adequate pH and its further buffer solution would provide a conventional physico-chemical ambient, where any result might sound normal.

Best regards

Marcos Nobre

Thanks professor Marcos  for your detailed answer.

Dear Y.Manoj Kumar,

can you give us, please, some infos about your cells (and the electrodes) ?

Dear Prof. Ioannis Samaras

Thanks for your response. here with i have given the details of the experiment.

All cyclic voltammetry experiments were performed in a single compartment cell with a three electrode configuration on a Princeton EG and G-PARC model potentiostat. Glassy carbon was the working electrode, saturated calomel as the reference electrode and the platinum wire was auxiliary electrode. The supporting electrolyte was 50 mM NaCl/ 5 mM Tris- HCl buffer at pH 7.1. The electrode surfaces were freshly polished with alumina powder and then sonicated in ethanol and distilled water for 1 min prior to each experiment and the electrode was rinsed with doubly distilled water thoroughly between each polishing step. Before the experiments, solutions were deoxygenated by purging with nitrogen gas for 15 min prior to the measurements.

 i want  to give more clarification in my doubt so that you can give your answer in correct way. In the CV, first i have taken the CV spectra for metal complex in solution  and i added the DNA to the solution then i take the reading. Based on the shift and current intensity we can say the mode of interaction between DNA and complexes.

In the present case the current intensity decreased along with positive shif. It indicate the mode of interaction between DNA and complex is intercalation. (there are many reference reports available for this concept). But here the question is why the current intensity decreases in the cathodic peak, but not in the anodic one.

Is DNA  interaction facilitate the cathodic current (reduction of Cu(II) to Cu(I)) and restrict the anodic current (oxidation of Cu(I) to Cu(II)) ?

i have attached the  CV spectra along with the question. see above.i am waiting for your response.

Dear Y.Manoj Kumar,

find, please, additional experimental support towards the proposal interpretation of Prof. George Zheng chen.

 Dear Y.Manoj Kumar,

As Prof. Samaras mentioned, my explanation is a proposal which is however based on the principle of what is known as electrochemical molecular recognition. The following is review article on this topic.

Beer PD, Gale PA, Chen GZ, Electrochemical molecular recognition: pathways between complexation and signalling, J. Chem. Soc. Dalton Trans., (1999) 1897-1909

Dear Y. Manoj Kumar,

Indeed I agree to the proposal of Prof. Chen regarding the selective complexing of DNA to the Cu(II) complex which also will depend on the pH of your electrolyte. Just for curiosity, change the pH to more acidic to observe any difference in the CV. 

This article might help: Zimmer, Ch, et al. "DNA–copper (II) complex and the DNA conformation." Biopolymers 10.3 (1971): 441-463.